(1) Field of the Invention
This invention is in the field of cased telescoped ammunition rounds, and more particularly relates to improvements to the cartridge case of such a round to facilitate removal of a fired cartridge case from the chamber of a gun.
(2) Description of Related Art
Cased telescoped ammunition in which the projectile is completely enclosed, or telescoped, within the cartridge case, reduces the volume and weight of a gun system firing cased telescoped ammunition compared with the weight and volume of a gun system using conventionally shaped ammunition rounds having an equivalent rate of fire. The reduced weight and volume for equivalent fire power makes such gun systems desirable for mounting in aircraft, tanks, and other mobile combat vehicles. In this application a gun system is defined to include a gun and its associated ammunition storage and feed subsystems. The benefits of using cased telescoped ammunition in a gun system derive primarily from the cylindrical shape of the cartridge case of each such round.
When a cased telescoped ammunition round is fired, the projectile is initially accelerated by a booster charge to close, or to obturate, the barrel of the gun before the main propellant charge is ignited. A control tube is commonly used to control the initial movement of the projectile. A booster charge is located in the control tube and is separated by the tube from the main propellant charge. Products of the ignited booster charge are initially confined within the control tube by a booster piston attached to the base of the projectile. Main charge ignition, thus, does not occur until the advancing piston clears the tube or exposes, or unblocks, ignition ports in the wall of the control tube which permits products of the burning booster charge to ignite the main charge. Ignition of the main charge is controlled by the position of the projectile and its booster piston relative to the control tube.
The external surfaces of the cartridge case of a typical cased telescoped ammunition round are formed by a cylindrical outer casing, or skin, and two caps, or end seals, a front seal and a rear seal. Each such round is loaded into a cylindrical gun chamber, or chamber, of the gun from which the round is to be fired and from which the spent cartridge case is removed, or unloaded, after firing and before another cycle of loading, firing, and unloading begins. In guns from which such rounds are typically fired, the chamber housing in which a number of gun chambers may be formed can take the form of a cylinder which is rotated about its axis of symmetry similar to the rotation of the cylinder of a hand held revolver, for example. In such a gun system the rounds are mechanically loaded into a given gun chamber when that chamber has a given orientation, position or station, relative to the gun barrel. The chamber housing is then rotated to bring the gun chamber into which a round has been loaded into alignment with the gun barrel ready for firing. After firing, the chamber housing is again rotated to another position so that the gun chamber with the cartridge case of the fired round, the spent cartridge case, can be removed from the gun chamber. Alternatively, the chamber housing may be moved linearly with respect to the gun barrel to position a gun chamber in a loading station where a round can be loaded into the chamber. The chamber housing is then moved to align the loaded gun chamber with the gun barrel. When the round is fired, the chamber housing is moved so that the gun chamber with the spent cartridge case is at its unloading station and the spent cartridge case is removed from the chamber prepatory to another round being loaded into it. In such a gun, the loading and unloading stations for a given chamber may be the same. Cased telescoped ammunition obviously can also be fired from more conventionally operating guns firing projectiles of from 20 to 45 mm, for example.
When the interior of the cartridge case is pressurized by the burning of the propellant within the cartridge, the outer skin, or outer casing, and the end seals function to prevent gun gas from escaping between the the chamber housing and the breech and barrel faces of the the gun. The pressure created by the burning propellant forces the end seals apart until they are constrained by the breech face of the gun forming one end of the gun chamber and by the the barrel face of the gun barrel which forms the other end of the gun chamber. This pressure also forces the lips of the end seals and the outer casing, or skin, of the cartridge case radially outward into intimate contact with the inner cylindrical surface of the gun chamber formed in the chamber housing. After such contact has been achieved, the pressure produced by the burning propellant acts to elastically deform the chamber housing, enlarging the diameter of the gun chamber and forcing apart the breech face and the barrel face of the gun. When the pressure within the cartridge case is relieved after the projectile exits the muzzle of the gun barrel, the gun and the chamber revert to their unpressurized dimensions. However, changes in the dimensions of the cartridge case experienced during firing can cause nonelastic changes in the dimensions of the cartridge case, so that the dimensions of the cartridge case do not return to the dimensions they possessed prior to the round being fired.
To extract a spent cartridge case after it has been fired, it is necessary in a gun with a movable chamber housings to move the chamber housing so that the gun chamber in which the spent cartridge case is located can be moved to its unloading position, or station. For such movement to take place as quickly as possible while requiring the minimum amount of force to accomplish such movement, it is necessary that there be sufficient clearance between the end seals of the spent cartridge and the breech face and the barrel face of the gun to minimize frictional resistance to the movement of the chamber housing. To quickly and easily remove the spent cartridge case from the gun chamber, it is important that the cartridge casing not press against the inner cylindrical surface of the gun chamber and that the spent cartridge case be sufficiently intact so that all components of the spent cartridge case can be removed together, or as an entity.
Because the elastic deformation occurring in a gun firing cased telescoped ammunition is so large, there is a need for an improved cartridge case for a cased telescoped ammunition round that provides adequate and proper clearance between the end seals and the breech face and the barrel face of the gun after the round has been fired as well as between the cartridge casing and the surface of the gun chamber while maintaining the integrity of the spent cartridge casing to facilitate its removal.
To reduce the pressure exerted by the outer casing, or skin, of a spent cartridge case of such a round on the surface of the gun chamber within which the round is fired, and thus the force needed to remove the spent cartridge case, the skin, or outer casing, can be designed to split longitudinally when fired which minimizes any pressure exerted by the outer casing against the inner surfaces of the gun chamber after the gun chamber returns to its initial dimensions, the dimensions it had immediately prior to the round being fired. In such rounds the end seals are free to move relative to the outer casing which requires special means to maintain the integrity of the casing i.e., the necessary degree of connection between the end seals and the split casing so that they can be removed as a single entity. Typically, the joint between the end seals and the casing includes a sealant to prevent moisture and contaminants from entering the round, but such joints are not strong enough to maintain the integrity of a spent cartridge case with the degree of reliability required so that the problem of removing a spent cartridge case as a single entity quickly, and completely with a minimum amount of energy is not consistently achieved.